I have a Macbook 13 inch Mid 2012, 4GB RAM and 1600 MHz DDR3) updated to Yosemite (no clean install), and am experiencing the same problem with my Bose Sound Link Mini as well as with my Logitech device, both working properly before.
I just tested the fix minnerman suggested, it seems like my bluetooth audio works without any lag so far. Although it doesn't really seem to make sense since Bluetooth traffic should be higher after this fix.
Maybe the conversion to lower sound qualities in order to reduce Bluetooth traffic is the problem rather than the Bluetooth connection itself?
I'll write again in a couple of days after testing the sound extensively.